An ultrahigh frequency wireless communication system based on mmWave is configured to operate at a center frequency of several GHz to several tens of GHz. Due to such a characteristic of the center frequency, in a mmWave communication system, a pathloss may appear noticeably in a radio shadow area. Considering such a pathloss, it is necessary to improve a random access procedure between a user equipment (UE) and a base station (BS). Moreover, in case that a plurality of user equipments exist, it is necessary to design a random access procedure by considering possibility of potential collision between RACH (random access channel) signals.